Needle-free injection represents an alternative route for drug administration that is free of many of the problems associated with the use of needles (AntaresPharma 2005; Balzer et al. 2001). Needle-free injectors (NFIs) operate by creating a high pressure jet of fluid/powder that penetrates the skin. Delivery is rapid (typically <0.5 s) which reduces apprehension while enhancing patient acceptance and ultimately compliance. In addition, NFIs have been shown to improve the efficacy of certain medications (Taylor et al. 1981; Jackson et al. 2001; Williams et al. 2000). Current NFI injectors use springs or compressed inert gases to propel fluid through the skin and into the underlying tissue. This affords minimal control over the pressure applied to the drug during the time course of the injection, parameters shown to be integral to determining the depth and dispersion of drug delivered (Wendell et al. 2006; Shergold et al. 2006), and hence its absorption into the circulation. Others have incorporated some pressure pulse shaping by using variable orifice gas valves or fast/slow pyrotechnic charges. More recently, Stachowiak et al. (2009) have used piezoelectric actuators for dynamic control of delivery, accomplished at the expense of a limited piston stroke and volume of fluid delivered.
An alternative approach to jet drug delivery is to store energy in electrical form and impose a time varying pressure profile (waveform) on the drug volume through the use of a monitored and servo-controlled electromechanical actuator such as a linear Lorentz force actuator. A moving coil Lorentz-force actuated NFI has been developed (U.S. application 11/354,279, filed Feb. 13, 2006 and published as U.S. Patent Publication No. 2007/0191758, the entire teachings of which are incorporated by reference herein). The inherent bi-directionality of the actuator allows the applied pressure to be controlled and even reversed when necessary.